Boeing has repaired the Ethiopian Airlines 787 Dreamliner that was severely damaged in a fire at Heathrow Airport and the jet is back in passenger service with the airline.

Boeing spokeswoman Kate Bergman said Wednesday that “the repair and refurbishment took approximately two months and has returned the airplane to full structural integrity, with no degradation to passenger safety or comfort.”

After some test flights in England, the airplane returned to passenger service just before Christmas.

Flightaware, which tracks airplane flights, shows the jet on a Dec. 23 scheduled flight from Frankfurt, Germany, to Ethiopian’s base in Addis Ababa.

Because it’s the first major repair to an airliner made largely from carbon-fiber-reinforced plastic composite, the method and efficacy are of intense interest to the airline industry and especially 787 operators.

The fire broke out July 12 when the airplane was parked and empty.

Investigators say it was likely caused by the incorrect installation of a small lithium battery inside an Emergency Locator Transmitter (ELT), an electronic device that transmits location data to satellites in the event of a crash.

The same device is used in most Airbus and Boeing jets, as well as other aircraft made by ATR, Dassault and Lockheed Martin.

The fire caused intense heat damage above the ceiling at the back of the passenger cabin. It scorched a large area of the carbon-fiber skin on the crown of the fuselage in front of the vertical tail fin.

People with knowledge of the repair method said Boeing fabricated a full rear fuselage barrel in its North Charleston, S.C., factory, then cut out a large patch to replace the fire-damaged skin of the Ethiopian jet. It began inserting the patch in mid-October.

Bergman declined to give any details of the repair method.

The United Kingdom Air Accident Investigation Branch (AAIB) continues to investigate the fire’s cause but has released no information since a bulletin a few days after the incident.

That bulletin recommended the disabling of the ELT device in all Boeing 787s until further notice.

Subsequently, aviation regulators ordered airlines worldwide to inspect the ELTs in other airplanes to check for wiring discrepancies.